The present invention relates to a conveyor construction, and more particularly, to a magnetic coupling assembly which automatically disengages a conveyor roller from a power drive for the accumulation of parts transported by the conveyor.
Conveyor systems are known which have one or more power driven rollers. In a factory, various parts are placed onto a conveyor to be transported to various locations in a plant, and it is common to have an accumulation of parts which are not taken off the conveyor as quickly as they are put onto the conveyor or are metered for control reasons. The conveyor driving mechanism, conveyor rollers, or the parts themselves may be damaged if the conveyor is continuously powered, and it is not stopped when an accumulation occurs. Thus, it is desirable to provide some means for stopping the conveyor rollers when an accumulation or metering of the items being transported occurs.
Manual controls may be used to stop the conveyor when an accumulation occurs, but an operator is required full-time to watch over the conveyor system and to actuate the controls when necessary. This is not desirable because it is an expensive use of personnel who could be used for other jobs. Further, the additional controls required are expensive and are subject to failure.
Slip clutches have been provided heretofore for the purpose of achieving slippage between driving and driven components when the torque transmitted therebetween reaches a predetermined level. Such previous clutch arrangements have included the use of a plurality of friction disks pressed axially together by force applying means such as springs. Other arrangements employed heretofore include the use of a spring component rigidly fixed to an input roller and frictionally associated with an output roller to slip relative thereto when a predetermined torque is applied to the output roller. In addition to such mechanical arrangements, magnetic and electromagnetic clutches have also been employed to provide slippage between input and output components.
Several disadvantages are attendant to the mechanical and electromechanical slip clutch arrangements heretofore provided. In this respect, friction disk and spring arrangements are subject to physical wear during use which decreases the capability thereof to provide for slippage at a desired torque level. More particularly, as the components of these arrangements wear, slippage occurs at a progressively lower level. Accordingly, frequent adjustment or replacement of parts is required. With electromagnetic slip clutches, an external source of excitation must be provided to obtain the magnetic field for energizing the clutch assembly. This, of course, requires the provision of appropriate electrical connections to the clutch assembly which, together with the provision of an external source of excitation often results in an undesirable complex assembly. Moreover, the level of excitation can vary, whereby slippage can occur at torque levels other than the desired level.
In accordance with the present invention, the foregoing disadvantages, and others, of slip clutches heretofore known are overcome. More particularly, the magnetic coupling assembly of the present invention advantageously provides a substantially constant magnetic force between the driving and driven components whereby slippage is achieved at a substantially constant torque level. Further, the magnetic force is completely internal whereby external excitation is not required and physical wear of the clutch components is essentially non-existent.